This application claims the Paris convention priority of Japanese Patent Application Nos. 2000-074582 and 2000-184005 filed on Mar. 16, 2000 and Jun. 20, 2000, respectively, which are incorporated herein by reference.
The present invention relates to a negative electrode for a lithium secondary battery, and more particularly, it relates to improvement of a negative electrode active material for the purpose of providing a negative electrode for realizing a lithium secondary battery having large discharge capacity and exhibiting very good charge-discharge cycle performance.
When a plate of metallic lithium is used as the negative electrode of a lithium secondary battery, dendritic lithium with activity is deposited during charge. The deposited lithium may react with the electrolyte so as to lower the capacity of the negative electrode or may further grow during repeated charge and discharge so as to cause internal short-circuit. When a plate of lithium-aluminum alloy prepared by electrochemically alloying lithium and crystalline aluminum is used instead of a metallic lithium plate, it is possible to suppress the reaction between lithium and the electrolyte and the growth of the dendritic lithium during repeated charge and discharge, resulting in improving the charge-discharge cycle performance. However, since the reaction rate of the electrochemical reaction (alloying reaction) between lithium and crystalline aluminum is low, the charge-discharge cycle performance cannot be largely improved.
As a negative electrode for a lithium secondary battery for further improving the charge-discharge cycle performance, a plate of lithium-aluminum alloy prepared by electrochemically alloying lithium and amorphous aluminum has been proposed (Japanese Laid-Open Patent Publication No. 63-13267/1988). According to this publication, the electrochemical reaction between lithium and amorphous aluminum is more rapidly proceeded than the electrochemical reaction between lithium and crystalline aluminum occurring in charge, and hence, the charge-discharge cycle performance can be largely improved.
As a result of examination, however, the present inventors have found the following: When a plate of lithium-aluminum alloy is used, inactive Li2O is deposited on the negative electrode because the contact area (reaction area) between the alloy and the electrolyte is small. As a result, the charge-discharge efficiency is so degraded that satisfactory discharge capacity and charge-discharge cycle performance cannot be obtained.
Accordingly, an object of the invention is providing a negative electrode for realizing a lithium secondary battery having large discharge capacity and exhibiting very good charge-discharge cycle performance.
The negative electrode for a lithium secondary battery of this invention (present electrode) includes, as a negative electrode active material, substantially amorphous aluminum alloy in the form of a powder with an average particle size of 50 xcexcm or less represented by a composition formula, Al100-xMx, in which M is at least one element selected from the group consisting of La, Y, Yb, Ce, Gd, Nd, Sm, Pr, Er, Ni, Co, Cu and Fe; and 1xe2x89xa6xxe2x89xa620.
As a result, the present invention provides a negative electrode for realizing a lithium secondary battery having large discharge capacity and exhibiting very good charge-discharge cycle performance.